As shown in JP-2001-082230A, an accumulator-type fuel supply apparatus is employed for injecting a fuel into a combustion chamber of a direct-injection engine such as a diesel engine. The fuel supply apparatus includes a pump unit and an electronic control unit (ECU) as described below.
The pump unit includes a high-pressure pump which suctions the fuel, pressurizes the fuel, and discharges the fuel into the accumulator. An amount adjusting unit adjusts the amount of fuel that the high-pressure pump suctions. Further, the amount adjusting unit increases or decreases the fuel amount that the high-pressure pump suctions in accordance with an amount of electric power supplied to the amount adjusting unit. Also, the amount adjusting unit adjusts the fuel amount that the high-pressure pump discharges.
The amount adjusting unit has control characteristics, which are stored in the ECU. The control characteristics are used for controlling the electric power supplied to the amount adjusting unit. The control characteristics indicate a correlation between the amount of electric power and a discharge amount of the high-pressure pump. The ECU operates the amount adjusting unit to control a fuel pressure in the accumulator. The fuel pressure in the accumulator corresponds to a fuel injection pressure into the combustion chamber. More specifically, the ECU calculates a requesting value required for bringing the fuel pressure in the accumulator to substantially agree with a target value. Then, in view of the control characteristic, the ECU calculates a target amount of electric power.
A fuel injector is mounted on each cylinder of the internal combustion engine. The ECU controls an injection timing and an injection period, so that the fuel amount injected into the combustion chamber agrees with a target fuel amount.
The fuel supply apparatus needs to fill the accumulator with the fuel at the time of starting the internal combustion engine. Therefore, the control characteristic of the pump units (hereinafter, referred to as master characteristic), which is corrected for starting the engine, is memorized in the ECU. For example, when assembling the fuel supply apparatus to a vehicle, a test is conducted so that an engine speed, a fuel pressure in the accumulator, a fuel injection amount and the like satisfy the conditions for starting the fuel supply apparatus. Therefore, the master characteristic is corrected on the basis of the result of the test, and the corrected control characteristic is stored in the ECU as a starting characteristic specific for individual pump unit.
However, the starting characteristics need to obtain for each of the individual pump units, and hence a tact time in a factory is obliged to increase. The starting characteristics of the pump units need to be acquired again and memorized again at the time of replacement of the pump unit in the market as well.